22 - Typical atrioventricular bypass tracts

Abstract

Bypass tracts (BTs) are remnants of the atrioventricular (AV) connections caused by incomplete embryological development of the AV annuli and failure of the fibrous separation between the atria and ventricles. There are several types of BTs, according to the structures they connect, including atrioventricular, atrionodal, atrio-Hisian, atriofascicular, fasciculoventricular, and nodofascicular BTs. In the Wolff-Parkinson-White (WPW) syndrome, AV conduction occurs, partially or entirely, through an AV BT, which results in earlier activation (preexcitation) of the ventricles than if the impulse had traveled through the AVN. Concealed AV BTs refer to AV BTs that conduct only in the retrograde direction and therefore do not result in ventricular preexcitation. AV reentrant tachycardia (AVRT) is a macroreentrant tachycardia with an anatomically defined circuit that consists of two distinct pathways, the normal AV conduction system and an AV BT, linked by common proximal (atrial) and distal (ventricular) tissues. Atrial tachycardia, atrial fibrillation, and AV nodal reentrant tachycardia can all coexist with a BT, whereby the BT serves as a bystander route for AV activation. The prevalence of WPW pattern on the surface ECG is 0.1% to 0.3% in the general population. The prevalence of the WPW syndrome (i.e., the combination of ventricular preexcitation and either a documented tachyarrhythmia or symptoms of a tachyarrhythmia) is substantially lower than that of the WPW ECG pattern. Catheter ablation is considered the treatment of choice for patients with the WPW syndrome. Catheter ablation is curative in more than 95% of patients with a relatively low complication rate.